One form of vacuum pump used in high vacuum systems, such as semiconductor processing systems, is the turbomolecular pump. A turbolaolecular pump comprises a high speed turbine which drives the gas molecules. Since the turbomolecular pump operates most efficiently in the molecular flow region, the gas molecules which are driven through the pump are removed by a roughing vacuum pump which maintains a vacuum in the order of 10.sup.-3 torr at the foreline, or exhaust, of the turbomolecular pump.
Because the gas as being pumped by the turbomolecular pump may be extremely corrosive or hazardous in other ways, it is often diluted by a purge gas in the foreline region of the pump. To that end, a purge valve is coupled to the pump to introduce purge gas from an inert gas supply. The purge gas is typically introduced into the motor/bearing region.
During shutdown of the pump, gas is typically introduced about the turbine blades through a separate vent valve. The vent gas prevents back streaming of hydrocarbons from the bearing lubricants in the foreline and assists in slowing of the pump by introducing a fluid drag.
To allow the turbomolecular pump to operate more effectively, some systems use a heater blanket about the housing to warm the blades and[housing during operation and to thus evaporate any condensed gases. During continued operation, cooling water is circulated through the pump to prevent overheating of the bearings. Typical systems include a sensor for sensing bearing temperature in order to provide a warning with overheating.
A rack mounted control box is generally used to convert power from a standard electrical outlet to that required by the pump drive motor. The motor driving the turbine is typically a DC brushless motor driven through a speed control feedback loop or an AC synchronous motor. More sophisticated controllers may be connected to the various valves of the system to open and close those valves according to some user programmable sequence. Leads from the controller are coupled to the pump drive motor, the temperature sensor and each valve to be actuated.